The present invention claims priorities from Japanese Patent Applications No. 9-286310 filed Oct. 20, 1997 and No. 9-295066 filed Oct. 28, 1997, which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a multi-mode antenna which has multiple working frequencies and polarizations.
2. Description of Related Art
Although a multi-mode antenna which can be used for various communication systems, including a terrestrial system and a satellite system, is desirable no possible solution for such a multi-mode antenna has been proposed but by combining existing available antennas.
FIG. 1 shows an example of a possible combination based on existing available antennas. In this example, a monopole antenna 101 (see "Mobile antenna Systems handbook", Fujimoto and James, Artech House 1994, pp.154-155) and a helical antenna 102 (see pp. 455-457 of the above-mentioned handbook) are mounted on a body 103 of a mobile terminal such as a handy-phone with a distance D.sub.111 . The monopole antenna 101 is in this case dedicated to the terrestrial communication system, such as GSM, and the helical antenna 102 is for the satellite type of communication with a circular polarization. The distance D.sub.111 has to be optimized for non perturbation of each diagram.
FIG. 2 shows another example of a combination of a PIFA antenna 201 (see pp. 235-239 of the above-mentioned handbook) mounted behind a body 203 of the handy-phone. Above the same body 203, an helical antenna 202 is mounted and separated from the other antenna 201. The PIFA antenna 201 is in this case dedicated to the terrestrial communication system, and the helical antenna 202 is for the satellite type of communication with a circular polarization. The placement of each of the antennas has to be optimized for the best performance.
One problem of prior art is that is uses multiple antennas, in fact one per application desired, this is then consuming a lot of space which is not suitable for integration on small portable devices. The cost of machining the structure also can increase since the structure is using separated antennas on the structure and location of antennas interaction between each of them has to studied each time. It requires a long investigation and trimming time.
Another problem of prior art is that most antenna structures are bulky and large so that the size of the antenna may become a critical point of the size of a mobile terminal. If the terminal needs to use more than one of the antennas, these antennas have to be combined on one body of the terminal multiplying the space consumed.
Further problem is that users have to determine from which system, either satellite or terrestrial,the terminal is receiving the call and which antenna should be pulled out for use. This is not so practical.